1. Field of the Invention
The present invention relates to a projection apparatus, and more particularly, to a projection apparatus having a projection lens with at least three aspherical lenses.
2. Description of the Prior Art
With the progress of science and technology, projection apparatuses gradually play an important role in use of family, entertainment or business. Traditional projection apparatus is composed of an image generation device and a projection lens. The image generation device generates an image, and the image is enlarged and projected on a projection screen.
Since the lenses of the projection lens is manufactured to have spherical surface before, the projection lens requires having many lenses to solve problems of aberration and image blur, so that size and weight of the projection lens is unable to be minimized. Please refer to FIG. 1, which is a schematic diagram illustrating a projection lens according to the prior art. As shown in FIG. 1, the projection lens 10 of the prior art uses fourteen lenses 12 to eliminate aberration and distortion of image in order to be suitable to the image generation device having a diagonal line larger than 0.4 inches, and lens surfaces of each lens 12 are spherical lens surfaces, so that number of the lenses 12 of the projection lens 10 is rapidly increased when a focal length is gradually reduced. However, the projection apparatus is tended to have characteristics of light weight and small size, so that the excess of the lenses of the projection lens would limit the volume of the projection device to be unable to be reduced. Furthermore, the weight of the projection device would likely be too heavy and causes user burden.
Accordingly, to provide a projection apparatus with large projection view angle, small size and light weight is an important objective in this field.